Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. Chapter 4 Radiation Biology

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 2 Dental Radiography  Questions  How does radiation damage cells?  What are the differences between short- and long- term effects of radiation damage?  What are the exposure risks of dental radiation?

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 3 Dental Radiography  Chapter 4 Reading:  Iannucci & Howerton (pp )

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 4 Dental Radiography  Chapter 4 Outline  Radiation Biology  Radiation Injury  Radiation Effects  Radiation Measurements  Radiation Risks

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 5 Introduction  Purpose  To describe the mechanisms and theories of radiation injury  To define the basic concepts and effects of radiation exposure  To detail radiation measurements  To discuss the risks of radiation exposure

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 6 Radiation Injury  Mechanisms of injury  Theories of radiation injury  Dose-response curve  Stochastic and nonstochastic radiation effects  Sequence of radiation injury  Determining factors for radiation injury

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 7 Mechanisms of Injury  Iannucci & Howerton (p. 35)  Some x-rays do not reach the dental x-ray film; they are absorbed by the patient’s tissue.  Chemical changes occur that result in biologic damage.  Two mechanisms of radiation injury are possible.  Ionization  Free radical formation

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 8 Ionization  Iannucci & Howerton (p. 35) (Fig. 4-1)  Results when x-rays strike patient tissue  Produced through the photoelectric effect or Compton scatter  Results in formation of a positive atom and dislodged negative electron  This electron will interact with other atoms within the absorbing tissues causing chemical changes within the cell that results in biologic damage.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 9 Free Radical Formation  Iannucci & Howerton (p. 35) (Figs. 4-2, 4-3)  Cell damage occurs primarily through formation of free radicals.  Free radicals are formed when an x-ray photon ionizes water.  Free radical An uncharged atom or molecule that exists with a single, unpaired electron in its outermost shell An uncharged atom or molecule that exists with a single, unpaired electron in its outermost shell Highly reactive and unstable Highly reactive and unstable

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 10 Theories of Radiation Injury  Iannucci & Howerton (pp )  Damage to living tissue caused by exposure to ionizing radiation may result from  A direct hit and absorption of an x-ray photon within a cell  Absorption of an x-ray photon by water within a cell accompanied by free radical formation  Two theories to describe how radiation damages biologic tissues  Direct theory  Indirect theory

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 11 Direct Theory  Cell damage results when ionizing radiation directly hits critical areas within the cell.  This occurs infrequently.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 12 Indirect Theory  X-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell.  When x-ray photons are absorbed by water within a cell, free radical formation results.  The free radicals combine to form toxins that damage cells.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 13 Dose-Response Curve  Iannucci & Howerton (p. 36) (Fig. 4-4)  Curve is used to correlate the damage of tissue with the dose of radiation received.  A linear, nonthreshold relationship is seen.  The linear relationship indicates that the response of the tissues is directly proportional to the dose.  The nonthreshold dose-response curve suggests that no matter how small the amount of radiation received, some biologic damage occurs.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 14 Stochastic and Nonstochastic Radiation Effects  Iannucci & Howerton (pp )  Stochastic effects  A direct function of the dose  No dose threshold; effects do not depend on the magnitude of the absorbed dose Examples - cancer and genetic mutations Examples - cancer and genetic mutations  Nonstochastic (deterministic) effects  Somatic effects that have a threshold; effects increase in severity with increasing absorbed dose Examples: erythema, loss of hair, cataracts, and decreased fertility Examples: erythema, loss of hair, cataracts, and decreased fertility

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 15 Sequence of Radiation Injury  Iannucci & Howerton (p. 37)  Latent period  The time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs  Depends on the total dose of radiation received and the amount of time it took to receive the dose  Period of injury  A variety of cellular injuries may result.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 16 Radiation Injury Sequence, Repair, and Accumulation  Iannucci & Howerton (p. 37) (Table 4-1)  Recovery period  Depending on a number of factors, cells can repair the damage caused by radiation.  Cumulative effects  Effects of radiation exposure are additive.  Unrepaired damage accumulates in tissues.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 17 Determining Factors for Radiation Injury  Iannucci & Howerton (p. 37)  Total dose  Dose rate  Amount of tissue irradiated  Cell sensitivity  Age

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 18 Radiation Effects  Short- and long-term effects  Somatic and genetic effects  Radiation effects on cells  Radiation effects on tissues and organs

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 19 Short- and Long-Term Effects  Iannucci & Howerton (p. 37)  Short-term effects  Associated with large doses of radiation in a short amount of time  Acute radiation syndrome (ARS) Includes nausea, vomiting, diarrhea, hair loss, hemorrhage Includes nausea, vomiting, diarrhea, hair loss, hemorrhage  Long-term effects  Small doses absorbed repeatedly over a long period of time  Effects seen after years, decades, or generations Cancer, birth abnormalities, genetic defects Cancer, birth abnormalities, genetic defects

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 20 Somatic and Genetic Effects  Iannucci & Howerton (pp ) (Fig. 4-5)  Somatic cells  All cells in the body except the reproductive cells  Genetic cells  The reproductive cells  Biologic effects of radiation can be classified as somatic or genetic.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 21 Somatic and Genetic Effects  Somatic effects  Seen in the person irradiated  Not seen in future generations  Genetic effects  Not seen in the person irradiated  Passed on to future generations

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 22 Radiation Effects on Cells  Iannucci & Howerton (p. 38) (Table 4-2)  A cell that is sensitive to radiation is termed radiosensitive; one that is resistant is termed radioresistant.  The response is determined by  Mitotic activity  Cell differentiation  Cell metabolism

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 23 Radiation Effects on Tissues and Organs  Iannucci & Howerton (p. 38)  Radiosensitive organs  Lymphoid tissue  Bone marrow  Testes  Intestines  Radioresistant tissues  Salivary glands  Kidney  Liver

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 24 Radiation Effects on Tissues and Organs  Iannucci & Howerton (p. 38)  Critical organ  An organ that, if damaged, diminishes the quality of a person’s life  Critical organs exposed during dental radiographic procedures include  Skin  Thyroid gland  Lens of the eye  Bone marrow

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 25 Radiation Measurements  Units of measurement  Exposure measurement  Dose measurement  Dose equivalent measurement

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 26 Units of Measurement  Iannucci & Howerton (p. 39) (Tables 4-3, 4-4)  Traditional (older) units of radiation measurement  Roentgen (R)  Radiation absorbed dose (rad)  Roentgen equivalent (in) man (rem)  SI (newer) units of radiation measurement  Coulombs/kilogram (C/kg)  Gray (Gy)  Sievert (Sv)

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 27 Exposure Measurement  Iannucci & Howerton (pp )  Roentgen  Roentgen measures radiation by determining the amount of ionization that occurs in air.  It does not describe the amount of radiation absorbed.  No SI equivalent  Exposure is stated in coulombs per kilogram.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 28 Dose Measurement  Iannucci & Howerton (p. 40)  The amount of energy absorbed by tissue  Traditional unit is the rad (radiation absorbed dose).  SI equivalent is the gray.  1 Gy = 100 rads

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 29 Dose Equivalent Measurement  Iannucci & Howerton (p. 40)  Dose equivalent measurement is used to compare biologic effects of different kinds of radiation.  Traditional unit is the rem (roentgen equivalent man).  SI equivalent is the sievert.  1 Sv = 100 rems

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 30 Measurements Used in Dental Radiography  Iannucci & Howerton (p. 40)  Milli means 1/1000  Used to express the small doses used in dental radiography

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 31 Radiation Risks  Sources of radiation exposure  Risk and risk estimates  Dental radiation and exposure risks  Patient exposure and dose  Risk versus benefit of dental radiographs

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 32 Sources of Radiation Exposure  Iannucci & Howerton (pp. 4-41) (Table 4-5)  Natural background radiation  A form of ionizing radiation that is ubiquitous in the environment Cosmic radiation Cosmic radiation  Stars and sun Terrestrial radiation Terrestrial radiation  Radioactive materials in the earth and air  In the United States the average dose of background radiation received by an individual ranges from 150 to 300 mrads per year.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 33 Sources of Radiation Exposure  Artificial or humanmade radiation  Resulting from modern technology Includes consumer products, fallout from atomic weapons, weapons production, and the nuclear fuel cycle Includes consumer products, fallout from atomic weapons, weapons production, and the nuclear fuel cycle Medical radiation including medical radiographic procedures, dental radiography, fluoroscopy, nuclear medicine, and radiation therapy Medical radiation including medical radiographic procedures, dental radiography, fluoroscopy, nuclear medicine, and radiation therapy

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 34 Risk and Risk Estimates  Iannucci & Howerton (p. 41)  The potential risk of dental radiography inducing a fatal cancer in an individual has been estimated to be 3 in 1 million.  The risk of a person developing a cancer spontaneously is much higher, or 3300 in 1 million.

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 35 Risk and Risk Estimates  Iannucci & Howerton (p. 41)  1 in a million risks of a fatal outcome  10 miles on a bicycle  300 miles in an auto  1000 miles in an airplane  Smoking 1.4 cigarettes a day

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 36 Dental Radiation and Exposure Risks  Iannucci & Howerton (p. 41)  Risk estimates  Thyroid gland  Bone marrow  Skin  Eyes

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 37 Patient Exposure and Dose  Iannucci & Howerton (pp ) (Table 4-6)  Film speed  Collimation  Technique  Exposure factors

Copyright © 2012, 2006, 2000, 1996 by Saunders, an imprint of Elsevier Inc. 38 Risk versus Benefit of Dental Radiographs  Iannucci & Howerton (p. 42)  Dental radiographs should be prescribed for a patient only when the benefit of disease detection outweighs the risk of biologic damage.  When dental radiographs are properly prescribed and exposed, the benefit of disease detection far outweighs the risk of damage.